The present invention relates to electronic devices with a solar cell.
There are electronic wristwatches which each include an EL (electroluminescence) element which enables the time appearing in a time display unit to be visually recognized at night and a slant switch which is turned on when the wristwatch is slanted in a specified direction so that the EL element is turned on to illumine the time display unit.
With such arrangement, only by slanting the wristwatch in a specified direction without operating the switch, the EL element is turned on. Although no illumination is required, the EL element is automatically turned on only by slanting slightly an arm on which the wristwatch is worn to thereby increase wasteful power consumption.
In order to avoid such problem, U.S. Pat. No. 5,612,931 discloses that the user operates a switch to select one of an EL element on mode in which when a slant switch is turned on, the EL element is turned on, and an EL off mode in which even when the slant switch is turned on, the EL element is not turned on.
However, in such arrangement, the switching operation is troublesome. The user can often forget the switching operation, and the EL element can remain turned on even when no illumination is required, and wasteful power would be consumed.
Electronic devices are manufactured and marketed which each include a solar cell whose output voltage charges a capacitor or a secondary battery whose voltage drives that solar cell.
When such electronic device is of a small type and can only include a capacitor and/or a secondary battery, and if the EL element is tried to be driven by the voltage of the capacitor or secondary battery, the capacity or battery would soon become dead because the charging capacity of the capacitor or secondary battery is small. Thus, it is required to minimize wasteful power consumption.